1. Technical Field
The present invention relates to a microcapsule, an electrophoretic display sheet, an electrophoretic display device, and an electronic apparatus.
2. Related Art
Generally, it is known that micro particles move (migrate) in a liquid by a coulomb power if an electrical field is applied to a dispersal system which micro particles are dispersed into a liquid. This phenomenon is called an electrophoresis. Recently, an electrophoretic display device by using this electrophoresis attracts attention as a new display device that can display desired information (image).
The electrophoretic display device includes a display memory and a wide viewing angle in a state without voltage application, and an ability of high-contrast display in low power consumption.
Since the electrophoretic display device is a nonemissive device, it is less harmful to eyes than an emissive display device such as a cathode-ray tube display.
As an electrophoretic display device like this, a micro capsule type device in which a plurality of micro capsules encapsulating electrophoretic particles (fine particles) and a liquid dispersion medium (a liquid), and a binder fixing each substrate and the micro capsules are arranged between a pair of substrates having electrodes is known.
For a consituant material of the microcapsule, a material with a high polarity such as gum arabic is generally used. On the other hand, for a constituent material of the electrophoretic particle encapsulated in the microcapsule, a polar group or the like is also adopted in order to add electric charge to the electrophoretic particle. Therefore, the microcapsule and the electrophoretic particle are easy to attach to each other, and this inhibits the migration of the electrophoretic particle.
To solve such a problem, a method to prevent a micro capsule and a electrophoretic particle from attaching to each other by covering an inner wall of the microcapsule with a surfactant including a hydrophobic functional group so that the inner wall of the microcapsule becomes a nonpolar state is disclosed. (e.g. JP-A-2003-1.40202)
However, the above-mentioned method cannot prevent a micro capsule and a electrophoretic particle from attaching to each other sufficiently as the surfactant is detached from the inner wall of the microcapsule as time passes. Further, another problem such as the detached surfactant attaching to electrophoretic particle arises. Therefore, the migration of the electrophoretic particle is inhibited. This causes a problem in which performance of the display function of the electrophoretic display device such as contrast is deteriorated.